Move FileEnumerator to its own file, do some refactoring.

content/browser/zygote_host/zygote_host_impl_linux.cc

Index: content/browser/zygote_host/zygote_host_impl_linux.cc
diff --git a/content/browser/zygote_host/zygote_host_impl_linux.cc b/content/browser/zygote_host/zygote_host_impl_linux.cc
index ba7884f856bcd6edc7bb2bdb224c89840947d826..c429a8248d8143ee92c4457658d41bcdb1fa413f 100644
--- a/content/browser/zygote_host/zygote_host_impl_linux.cc
+++ b/content/browser/zygote_host/zygote_host_impl_linux.cc
@@ -13,6 +13,7 @@
 #include "base/command_line.h"
 #include "base/environment.h"
 #include "base/file_util.h"
+#include "base/files/file_enumerator.h"
 #include "base/linux_util.h"
 #include "base/logging.h"
 #include "base/memory/linked_ptr.h"
@@ -371,8 +372,7 @@ void ZygoteHostImpl::AdjustRendererOOMScore(base::ProcessHandle pid,
 
   if (!selinux_valid) {
     const base::FilePath kSelinuxPath("/selinux");
-    file_util::FileEnumerator en(kSelinuxPath, false,
-                                 file_util::FileEnumerator::FILES);
+    base::FileEnumerator en(kSelinuxPath, false, base::FileEnumerator::FILES);
     bool has_selinux_files = !en.Next().empty();
 
     selinux = access(kSelinuxPath.value().c_str(), X_OK) == 0 &&